Low prequencey excitation circuit for barkhausen-noise studies



June 28, 1966 w. A. GEYGER 3,253,634

LOW FREQUENCEY EXCITATION CIRCUIT FOR BARKHAUSENNOISE STUDIES Filed April 7. 1964 n3 I09 8 F? E? :5 r 1 IF 5; ii E 99 2E 52- E 95 E 5 n9 0 97 93 E; g; I: II 123 I m IO! William A. Geyger INVENTOR.

BY NW ATTORNEY United States Patent LOW FREQUENCY EXCITATION CIRCUIT FOR BARKHAUSEN-NOISE STUDIES William A. Geyger, Takoma Park, Md., assignor t0 the United States of America as represented by the Secretary of the Navy Filed Apr. 7, 1964, Ser. No. 358,129

3 Claims. (Cl. 324--34) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to an apparatus for producing a low frequency voltage and more particularly to an apparatus for producing voltage having frequencies as low as cycle per second for use in studying Barkhausen noises in magnetic materials.

In 1919 it was discovered by H. Barkhausen, that in magnetizing iron or other ferromagnetic substances, the magnetization level changed in a series of minute jumps or steps. When a coil in addition to the magnetizing coil is placed on a ferromagnetic specimen and connected to an oscillograph or an audio amplifier, a succession of small voltage peaks may be detected on an oscillograph and clicking noises may be heard from a speaker or phone connected to the output of the audio amplifier.

In the study of saturable core materials it is desirable to provide a convenient means for energizing the magnetic or saturable core materials with a very low frequency voltage so that the Barkhausen effect for a particular core material may be analyzed. Ideally, a very low frequency voltage application will produce voltage changes which are more readily observable as the voltage peaks occur less rapidly than with normal frequency A.-C. power supply.

With the apparatus of the present invention, it is possible to provide voltages having frequencies as low as 4 cycle per second. The shaft of an A.-C. motor is mechanically connected to a synchro control transformer through a gear train. The speed of the AC. motor is varied by varying the voltage supplied to the motor. With such an arrangement, the shaft of the synchro control transformer may be rotated at speeds ranging from revolution per second to 4 revolutions per second in an exemplary embodiment of this invention. The rotor windings of the control transformer are connected to a source of A.-C. voltage and the stator windings are connected to a ring diode type demodulator. The output of the demodulator is fed through filter, phase shift and amplifier circuits to an air core coil which surrounds a toroidal core material to be tested. A winding on the toroidal core is connected to an oscilloscope or other indicator means such as an audio amplifier and speaker or earphone.

An object of this invention is to provide an apparatus for the study of Barkhausen noises in ferromagnetic materials.

Another object of this invention is to provide an A.-C. voltage source having a frequency as low as A cycle per second.

A further object of this invention is to provide a very low frequency voltage source for testing ferromagnetic core materials.

It is a still further object of this invention to provide apparatus for studying Barkhausen noise voltages in ferromagnetic materials in which a low frequency A.-C. voltage is used to supply a saturating field flux for the ferromagnetic material to be tested.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following de- Patented June 28, 1966 tailed description when considered in connection with the accompanying drawing wherein:

The single figure of this invention illustrates a preferred embodiment of the low frequency excitation circuit of this invention.

Referring now to the drawing, an A.-C. power source 11 is shown connected to power lines 13 and 15. Source 11 may be a llO-volt, 60-cycle power source, for example. A motor 17 is equipped with windings 19 and 21, Winding 19 is connected to lines 13 and 15 through capacitor 23. Winding 21 is connected to lines 13 and 15 through single winding transformer 25 having movable tap 27. A voltmeter 22 is connected across Winding 21 to indicate the voltage applied therethrough. The shaft of motor 17 is connected mechanically to the shaft of synchro control transformer 29 as indicated by dotted line 31. A gear train may be part of the mechanical connection such that the range of speed of the shaft of the synchro control transformer 29 may range from about A to 4 revolutions per second, for example. Other gear trains or speed reduction units may be employed in the mechanical connection 31 between motor 17 and synchro control transformer 29 to obtain a desired speed. Rotor terminals 33 and 35 of synchro control transformer 29 are connected to A.-C. lines 13 and 15 through transformer 37 having primary winding 39 and secondary winding 41. Transformer 37 operates to reduce the line voltage from 120 volts to 48 volts, for example. A stator winding of synchro control transformer 29 is connected to primary winding 43 of transformer 45 through stator terminals 47 and 49. The secondary winding 51 of transformer 45 is connected to terminals 53 and 55 of ring-type demodulator 57. Demodulator 57 is comprised of diodes 49, 61, 63 and 65, and resistors 67, 69, 71 and 73. A reference voltage is supplied to ring-type demodulator 57 by transformer 75. Primary winding 77 of transformer is connected to lines 13 and 15 and the secondary winding 79 is connected to terminals 81 and 83 of the ring demodulator circuit. The output of the ring demodulator is taken from center tap 85 of transformer 45 and center tap 87 of transformer 75. The output of the ring demodulator is connected to a filter circuit comprising capacitor 89, inductor 91 and resistor 93. The output of the filter circuit is connected to a phase shift circuit comprising capacitor 95 and resistor 97, and to terminals 99 and 101 which are connected to horizontal deflection input terminals 103 and 105 of oscilloscope 107. The output of the phase shift circuit is connected to input terminals 109 and 111 of an amplifier 113. Output terminals 115 and 117 of amplifier 113 are connected to air core coil or winding 119. A toroidal saturable core 121 to be tested is placed within air core coil 119. An output winding 123 on core 121 is connected to the vertical deflection input terminals 125 and 127 of oscilloscope 107.

In operation, A.-C. voltage source 11 supplies energy to transformers 25, 37, 75 and to winding 19 of motor 17, through lines 13 and 15. A.-C. voltage source 11 may be a -volt, 60-cycle source, for example. Winding 21 of motor 17 is energized through single winding transformer 25. The speed of motor 17, which is controlled by the setting of movable tap 27, determines the frequency of the output voltage. That is, the speed of motor 17 will control the shaft speed of the synchro control transformer which in turn determines the frequency of the voltage applied to demodulator 57. The output voltage from the synchro transformer is modulated voltage which is a mixture of the 60-cycle AC. voltage applied to the rotor terminal 33 of the synchro control transformer 29 and the low frequency amplitude variations caused by the rotation of the rotor windings of control transformer 29. The 60-cycle componentof the modulated voltage is removed by demodulator 57 and only the low frequency variations in amplitude due to the rotation of the rotor of control transformer is applied to center taps 85 and 87. The low frequency voltage thus formed is then applied to a filter circuit comprising capacitor 89, inductor 91 and resistor 93. This filter circuit acts to filter out 60-cycle frequency components which pass through demodulator 57. The low frequency voltage is then applied through terminals 99 and 101 to horizontal deflection input terminals 103 and 105 of oscilloscope 107. This voltage is also applied to a phase shift circuit comprising capacitor 95 and resistor 97. The phase shift circuit operates to shift the phase of the low frequency voltage applied to amplifier 113 90 degrees. The voltage at the output terminals 115 and 117 is applied to coil 119 to energize the coil and provide a low frequency magnetic field for alternately saturating core 121. Winding 123 is connected to vertical deflection input terminals 125 and 127 to provide an indication of the Barkhausen noise activity taking place within core 121 as it is alternately saturated by the magnetic field surrounding the core, Coil 123 may also be connected to a transducer device such as a speaker or earphone to produce audible indications of the Barkhausen noises as the core is being alternately saturated at a very low frequency as provided by the low frequency voltage applied to coil 119 from amplifier 113.

In a preferred embodiment of this invention a twophase motor was used to drive the shaft of synchro control transformer through a gear train. A speed range of A to 4 revolutions per second of the synchro control transformer shaft was provided. This range may be extended, if desired, to lower or higher speeds by changing gear ratios in the gear train or the speed range of the motor or both. The reference voltage applied to the secondary winding 41 may be 48 volts. Diodes 59, 61, 63 and 65 may be silicon diodes. The black diodes 59 and 61 indicate current flow for a particular half-cycle of energy, such as positive half-cycles for example and the white diodes 63 and 65 indicate current flow for particular alternate half-cycles such as negative half-cycles, for example. Resistors 67, 69, 71 and 73 may have a value of 5,000 ohms each. Capacitor 89 may have a value of microfarads. Inductor 91 may have a value of 100 henries, and resistor 93 may have a value of 8,000 ohms. Capacitor 95 may have a value of 40 microfarads and resistor 97 may have a value of 500 ohms. Amplifier 113 may be a D.-C. amplifier, for example. The low frequency excitation winding or coil 119 may be made of 10,000 turns of No. 36 wire having a total resistance of 1,800 ohms. The core 121 may be an ultra-thin tape bobbin core made from 80 Wraps of A; mil, A; inch tape with an inside diameter of 0.5 inch.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described,

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. Apparatus for studying Barkhausen noises in ferromagnetic materials comprising,

an A.-C. voltage source,

an electric motor connected to said A.-C. voltage source through a variable speed control means whereby the speed of said motor may be varied,

a control transformer having a stator with stator winding means, a rotor with rotor winding means, a shaft on said rotor,

gear train means connecting said motor shaft to said control transformer shaft whereby said rotor of said control transformer may be rotated at a speed of less than one revolution per second,

first transformer means connecting said rotor winding means to said A.-C. voltage source,

a ring diode demodulator circuit having a first diode,

a second diode, a third diode and a fourth diode, means serially connecting said first diode and said second diode with a first junction therebetween,

means serially connecting said second diode and said third diode with a second junction therebetween,

means serially connecting said third and fourth diodes with a third junction therebetween,

means serially connecting said third diode and said first diode with a fourth junction therebetween,

second transformer means having a primary winding and a secondary winding, said secondary winding having a center tap thereon,

third transformer means having a primary winding and a secondary winding, said secondary winding having a center tap thereon,

means connecting the primary winding of said second transformer means to said A.-C. voltage source,

means connecting the secondary winding of said second transformer means to said first and third junctions of said demodulator,

means connecting the primary winding of said third transformer to the stator winding means of said control transformer,

means connecting the secondary winding of said third transformer means to said second and fourth junctions of said demodulator,

means connecting said center tap of said second transformer means to a first input terminal of a filter circuit,

means connecting said center tap of said third transformer means to a second input terminal of said filter circuit,

means connecting a first output terminal of said filter circuit to a first horizontal deflection terminal of a cathode-ray oscilloscope,

means connecting a second output terminal of said filter circuit to a second horizontal deflection circuit of said oscilloscope,

a phase shifter having an input circuit and an output circuit,

means connecting said first and second output terminals of said filter circuit to said input circuit of said phase shift means,

an amplifier having an input circuit and an output circuit,

means connecting the output circuit of said phase means to the input of said amplifier,

a cylindrical coil means,

means connecting the output circuit of said amplifier to said coil means,

a saturable toroidal test core disposed within said coil means,

a winding on said core,

means connecting said winding to vertical deflection input terminals of said oscilloscope whereby Barkhausen noises of said core may be observed when said core is saturated slowly by a low frequency voltage applied to said coil from the output circuit of said amplifier.

2. A low frequency excitation circuit for the study of Barkhausen noises in ferromagnetic materials comprising,

an A.-C. voltage source,

a synchro control transformer having a rotor winding means and a stator winding means, said rotor Winding means, being mounted on a rotatable shaft,

means connected to said shaft to rotate said shaft at speeds from less than one revolution per second to greater than one revolution per second whereby a low frequency A.-C. voltage having a frequency from less than one cycle per second to greater than one cycle per second may be produced,

means connecting said rotor winding means to said A.-C. voltage source,

means connecting said stator winding means to input terminals of a demodulator circuit whereby said A.-C. voltage source component may be removed from the voltage across said stator windings,

means connecting output terminals of said demodulator circuit to input terminals of a filter circuit,

means connecting output terminals of said filter circuit to input terminals of phase shift means,

means connecting output terminals of said phase shift means to input terminals of an amplifier,

means connecting output terminals of said amplifier to a cylindrical coil,

means connecting the output terminals of said filter circuit to horizontal deflection input terminals of a cathode ray oscilloscope,

a toroidal saturable test core disposed Within said coil,

a winding on said core,

means connecting said winding to vertical deflection input terminals whereby Barkhausen noise voltages may be observed on said oscilloscope as a low frequency voltage provides a slowly increasing and decreasing flux around said core.

3. Apparatus for observing Barkhausen noise voltages in a ferromagnetic material comprising,

a low frequency A.-C. voltage source having a frequency ranging from less than one cycle per second to greater than one cycle per second,

an oscilloscope having horizontal deflection input terminals and vertical deflection input terminals,

a cylindrical coil,

a saturable toroidal test core disposed within said coil,

means applying said low frequency A.-C. voltage source to the horizontal deflection input terminals of said oscilloscope,

means applying said low frequency AC. voltage source to a phase shifter to shift the phase of said low frequency AC. voltage source by 90 degrees,

means connecting said phase shifter to an amplifier,

means connecting said amplifier to said coil whereby said core may be saturated and desaturated at a low frequency,

a winding on said core,

means connecting said winding to the vertical deflection input terminals of said oscilloscope whereby Barkhausen noise voltages from said core may be applied to said oscilloscope.

References Cited by the Examiner UNITED STATES PATENTS 2,098,064 11/1937 Pfaffenberger 32437 2,904,745 9/1957 Bugg 32434 3,197,693 7/1965 Libby 324-34 RICHARD B. WILKINSON, Primary Examiner. 

1. APPARATUS FOR STUDYING BARKHAUSEN NOISES TO FERROMAGNETIC MATERIALS, COMPRISING, AN A.-C VOLTAGE SOURCE, AN ELECTRIC MOTOR CONNECTED TO SAID A.-C VOLTAGE SOURCE THROUGH A VARIABLE SPEED CONTROL MEANS WHEREBY THE SPEED OF SAID MOTOR MAY BE VARIED, A CONTROL TRANSFORMER HAVING A STATOR WITH STATOR WINDING MEANS, A ROTOR WITH ROTOR WINDING MEANS, A SHAFT ON SAID ROTOR, GEAR TRAIN MEANS CONNECTING SAID MOTOR SHAFT TO SAID CONTROL TRANSFORMER SHAFT WHEREBY SAID ROTOR OF SAID CONTROL TRANSFORMER MAY BE ROTATED AT A SPEED OF LESS THAN ONE REVOLUTION PER SECOND, FIRST TRANSFORMER MEANS CONNECTING SAID ROTOR WINDING MEANS TO SAID A.-C VOLTAGE SOURCE, A RING DIODE DEMODULATOR CIRCUIT HAVING A FIRST DIODE, A SECOND DIODE, A THIRD DIODE AND A FOURTH DIODE, MEANS SERIALLY CONNECTING SAID FIRST DIODE AND SAID SECOND DIODE WITH A FIRST JUNCTION THEREBETWEEN, MEANS SERIALLY CONNECTING SAID SECOND DIODE AND SAID THIRD DIODE WITH A SECOND JUNCTION THEREBETWEEN, MEANS SERIALLY CONNECTING SAID THIRD AND FOURTH DIODES WITH A SECOND JUNCTION THEREBETWEEN, MEANS SERIALLY CONNECTING SAID THIRD DIODE AND SAID FIRST DIODE WITH A FOURTH JUNCTION THEREBETWEEN, SECOND TRANSFORMER MEANS HAVING A PRIMARY WINDING AND A SECONDARY WINDING, SAID SECONDARY WINDING HAVING A CENTER TAP THEREON, THIRD TRANSFORMER MEANS HAVING A PRIMARY WINDING AND A SECONDARY WINDING, SAID SECONDARY WINDING HAVINGA CENTER TAP THEREON, MEANS CONNECTING THE PRIMARY WINDING OF SAID SECOND TRANSFORMER MEANS TO SAID A.-C VOLTAGE SOURCE, MEANS CONNECTING THE SECONDARY WINDING OF SAID SECOND TRANSFORMER MEANS TO SAID FIRST AND THIRD JUNCTIONS OF SAID DEMODULATOR, MEANS CONNECTING THE PRIMARY WINDING OF SAID THIRD TRANSFORMER TO THE STATOR WINDING MEANS OF SAID CONTROL TRANSFORMER, MEANS CONNECTING THE SECONDARY WINDING OF SAID THIRD TRANSFORMER MEANS TO SAID SECOND AND FOURTH JUNCTIONS OF SAID DEMODULATOR, 